Anything is possible in poly. Why should you not get married and have other lovers? There are no rules. You get to decide.
Book stores generally have the ethical slut. A really good book if you are both into poly. Otherwise on line is the best bet.
Have a good read around here. Your story is just about a carbon copy of many others on here. Keep looking around and start with educating yourself. Then start planning and keep communicating.
Ari and Mono have excellent points.